With increasing industrial development, diverse electronic devices are used to achieve various purposes. An electronic device comprises a plurality of electronic components. Generally, different kinds of electronic components are operated by using different voltages.
As known, a power supply is essential for many electronic devices such as personal computers, industrial computers, servers, communication products or network products. Usually, the user may simply plug a power supply into an AC wall outlet commonly found in most homes or offices so as to receive an AC voltage. The power supply will convert the AC voltage into a regulated DC output voltage for powering the electronic device. The regulated DC output voltage is transmitted to the electronic device through a power cable.
FIG. 1 is a schematic block diagram of a conventional power conversion circuit. The conventional power conversion circuit 1 of FIG. 1 is a buck-type power conversion circuit. By the power conversion circuit 1, an AC input voltage VIN (e.g. from a utility power source) is converted into an output voltage Vo. As shown in FIG. 1, the power conversion circuit 1 principally comprises a rectifier circuit 11, a bootstrap circuit 12, a control circuit 13, a switching circuit 14, a feedback circuit 15, a diode D, an inductor L, a capacitor C and a current transformer CT. The AC input voltage VIN is rectified by the rectifier circuit 11 into a rectified voltage. The switching circuit 14 includes a switch element Q. A first terminal of the switching circuit 14 is connected to the output terminal of the rectifier circuit 11. A second terminal of the switching circuit 14 is connected to the bootstrap circuit 12. The switching circuit 14 is driven by the bootstrap circuit 12 so as to be conducted or shut off.
The detecting terminal of the current transformer CT is connected to the switching circuit 14 and the inductor L. The output terminal of the current transformer CT is connected to the control circuit 13 and a common terminal COM. When the switching circuit 14 is conducted, the current transformer CT can detect the current flowing through the switching circuit 14, thereby generating a detecting current signal to the control circuit 13. The inductor L is connected to the detecting terminal of the current transformer CT and the output terminal of the power conversion circuit 1. When the switching circuit 14 is conducted, electric energy is stored in the inductor L. Whereas, when the switching circuit 14 is shut off, the inductor L discharges the stored electric energy so as to generate the output voltage Vo. An end of the capacitor C is connected to the inductor L and the output terminal of the power conversion circuit 1. The other end of the capacitor C is connected to the common terminal COM. The capacitor C is used for filtering the output voltage Vo that is generated by the inductor L. The cathode of the diode D is connected to the inductor L and the current transformer CT and the anode of the diode D is connected to the common terminal COM, thereby forming a discharging path.
The feedback circuit 15 is connected to the output terminal of the power conversion circuit 1 and the control circuit 13. According to the output voltage Vo, the feedback circuit 15 generates a feedback signal to the control circuit 13. The control circuit 13 is connected to the bootstrap circuit 12, the output terminal of the current transformer CT and the feedback circuit 15. The control circuit 13 can generate a control signal. According to the control signal, the operation of the switching circuit 14 is driven by the bootstrap circuit 12. Furthermore, according to the detecting current signal transmitted from the current transformer CT, the control circuit 13 can detect whether an over-current phenomenon occurs. If the over-current phenomenon occurs, the switching circuit 14 is driven by the bootstrap circuit 12 to be shut off according to the control signal. According to the feedback signal transmitted from the feedback circuit 15, the duty cycle of the switching circuit 14 is adjusted, so that the magnitude of the output voltage Vo is maintained above a threshold value.
Although the conventional power conversion circuit 1 is effective to convert the AC input voltage into the output voltage, there are still some drawbacks. For example, since the switching circuit 14 of the power conversion circuit 1 is connected to the high-voltage terminal, the bootstrap circuit 12 is required to drive the switching circuit 14. As known, the switching circuit 14 is very costly and thus the overall cost of the power conversion circuit 1 increases. Furthermore, for filtering the harmonic waves and reducing the electromagnetic interference, the power conversion circuit 1 has an electromagnetic interference (EMI) filter circuit (not shown) connected to the input terminal of the power conversion circuit 1.
Furthermore, the distribution of the AC input current is very centralized during operation of the conventional power conversion circuit 1 and the peak values are relatively higher, higher harmonic waves are possibly generated. As such, the conventional power conversion circuit 1 should have a large-sized electromagnetic interference filter circuit for filtering the harmonic waves and reducing the electromagnetic interference. The use of the large-sized electromagnetic interference filter circuit will increase the fabricating cost of the conventional power conversion circuit 1. Moreover, since the distribution of the AC input current is very centralized, the power factor of the power conversion circuit 1 is too low. Due to the low power factor, the apparent input power is high and more power loss of the power conversion circuit 1 is consumed. Since the conventional power conversion circuit 1 generates the output voltage Vo by means of the single switching circuit 14 and the single inductor L, a great amount of heat is generated by the switching circuit 14 and the inductor L when the output voltage Vo is used for driving a high-power electronic device. Under this circumstance, the switching circuit 14 and the inductor L are possibly damaged due to an over-heating effect and the power conversion circuit 1 fails to be normally operated.
There is a need of providing a power conversion circuit for decentralizing an input current so as to obviate the drawbacks encountered from the prior art.